Thin film coating method and the manufacturing line for its implementation

ABSTRACT

A group of inventions is related to process equipment to process surfaces in mass production, particularly, vacuum process equipment to apply thin film coatings with set optical, electrical and other parameters. 
     The technical result is to ensure a capability of processing flexible large substrates, as well as small substrates with a high degree of coating uniformity, with an ability to utilize a wide range of technologies and process devices, as well as to have a highly effective useful operation of applied materials. 
     The proposed technical result is obtained by a method of applying thin film coatings on substrates, which are placed on rotating drums, which consequently move along the processing zones with the same constant linear and angular speeds. 
     Furthermore, a ratio between the linear and angular speeds of the drum is selected so that each surface point of the drum will complete at least two full revolutions while passing through the processing zone. 
     Also, the proposed technical result is also achieved by the fact that within the manufacturing line for applying the thin film coatings, consisting of the inlet airlock chamber, process chamber with at least one process device within it, which forms a processing zone, outlet buffer chamber, transportation system and substrate holder, designed to move along chambers, a substrate holder designed as a carriage with a cylinder installed on it, positioned coaxially toward the movement direction of the carriage and designed to rotate, while the angular rotational velocity and linear speed of the movement, during the processing, will be constant and selected so that each surface point of the cylinder will complete at least two full revolutions while passing through the processing zone. Furthermore, the transportation system will be equipped with rollers, and carriage with guides that interact with rollers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage patent application arising fromPCT/RU2014/000010 filed on Jan. 14, 2014, and referenced in WIPOPublication No. WO2015/108432. The earliest priority date claimed isJan. 14, 2014.

FEDERALLY SPONSORED RESEARCH

None

SEQUENCE LISTING OR PROGRAM

None

PERTINENT ART

This group of inventions is related to the process equipment field toprocess surfaces in mass production, particularly, vacuum processequipment, designated for thin film coating with set optical, electricaland other properties.

PREVIOUS TECHNOLOGY LEVEL

From the technical level, there are various methods of thin filmcoatings on processed goods (substrates).

U.S. Pat. No. 4,851,095, published in Jul. 25, 1989, describes themethod of magnetron deposition of thin film coatings on substrates,placed on a rotating drum. The coating deposition on substrates isimplemented by operating devices within the vacuum chamber around thedrum.

Deficiencies of this technical solution are low productivity andsignificant cost of goods due to the need to repeat process operationsto achieve the required quantity of layers in the structure.

The closest one by combination of significant features to the proposedmethod is shown in the U.S. Pat. No. 6,893,544, published on May 17,2005, a method of applying thin-film coatings, in which the substratesare fastened to a vertical flat carriage, moving in the linear type ofthe process equipment (magnetron deposition cathodes, linear sources ofplasma, etc.).

Deficiencies of this method are high cost and low productivity,especially when applying complex and precise coatings, due to the needto use complicated control systems and settings (i.e. overhead time andmaterials), high material consumption, due to the processing area of theprocess equipment is higher than the uniformity area, and, for example,during magnetron deposition, 30-50% of target material misses thesubstrate, as well as the limited zone of applicable process equipment,since we can only use such equipment that ensures an acceptableuniformity, which excludes a wide range of perspective technologies.

From this level of technology, we also know of various equipment forapplication of thin film coatings on processed goods (substrates).Particularly, to process small size substrates in mass production,periodic action drum devices are used, for example, such as a device,described in U.S. Pat. No. 4,851,095, published on Jul. 25, 1989, whichincludes a cylindrical substrate holder, with substrates around it.Coating uniformity in one direction is ensured by a drum rotation, whilein another direction by using linear process equipment.

In display production, where flat substrates are processed, an in-linetype of equipment is used. As an example of such equipment, wheresubstrates are fastened to the carriage, moving along subsequent processstages, we may refer to an automated device for forming thin filmcoatings, described in the patent of the utility model RU 78785,published on Dec. 10, 2008. However, this equipment, just like any otherequipment known today, has such deficiencies as low operationalreliability due to dependency of reliable fastening to substrates onsmooth movement of a transportation system, as well as high cost due tocomplex control systems and settings to ensure the required uniformityof application onto surfaces.

The closest one to this invention, by overall significant parameters, isthe process line for deposition of thin film coatings, described in U.S.Pat. No. 6,893,544, published on May 17, 2005, which includes theconsequently placed airlock chamber, processing chamber, with processingequipment within it, buffer chamber and flat substrate holder, designedto move along the chambers.

This technical solution has the following deficiencies:

Limited range of standard sizes of treatable substrates, particularly aninability to process flexible substrates, for example, thin glass due toan inability to ensure their reliable hold and protection when movingalong the manufacturing line;

high cost due to complicated control systems and settings, especiallyfor complex and precise coatings, as well as significant materialconsumption, 30-50% of which misses the substrate due to provision ofuniformity of deposited layer at the expense of the process zone ofmanufacturing equipment being larger than the uniformity zone;limited range of applicable technologies and process equipment, since apossible application is limited by requirements of acceptable uniformityof deposited layer.

DISCUSSION OF GROUP OF INVENTIONS

The challenge that a present group of inventions is focused on is thecreation of high-productivity unified equipment to process substrateswith a wide range of standard sizes.

When this challenge is solved, the technical result is achieved, whichensures the possibility of processing flexible large substrates, as wellas small substrates with high degree of uniform coverage with ability touse a wide range of technologies and process equipment, as well as withhigh efficiency of value-added use of applied materials.

The mentioned technical result is achieved by having a method ofapplying thin film coatings on substrates, which would be held byholders and consequently moving holders with substrates throughprocessing chambers, within which the coating is applied by processingequipment, located within processing chambers. Furthermore, thesubstrate holders are designed as rotating drums, which move through theprocessing zones of processing equipment, parallel to the rotating axisof the drums, and rotate with constant linear and angular velocities,while the ratio of linear and angular velocities is selected from thecondition that calls for every point of the drum surface would make atleast two full revolutions when going through a processing zone of theprocessing equipment.

The mentioned technical result is also achieved by having the thin filmcoating manufacturing line with airlock and buffer chambers, and atleast one processing chamber with processing equipment, substrateholders, positioned on carriages, installed as to have an ability topass through chambers, and transportation system. Furthermore, thesubstrate holders are designed as rotating drums, which move through theprocessing zones of processing equipment, positioned on the carriagecoaxially to the direction of its movement, and rotate with constantlinear and angular velocities, and ensuring at least two fullrevolutions of every point of the drum surface when going through aprocessing zone of the processing equipment.

To achieve this technical result, the manufacturing line may containinlet and outlet airlock and buffer chambers. Furthermore, the substrateholder carriage may be designed as a hanger, positioned above thesubstrate holder, or as a frame, or as a cart with linear guides,positioned under the substrate holder. The manufacturing line may alsobe equipped, at least, with one drive to rotate substrate holders.Substrate holders may be equipped with frictional and/or magneticremovable couplings and/or low voltage electric motor. Furthermore,every substrate holder may be equipped with an electric motor, thetransportation system may be equipped with rollers, and the carriage maybe equipped with guides that interact with rollers.

The principle of achieving uniformity, created by design, is explainedin the case of the description of the movement of the cylindrical holderthat makes an even rotating and forward movement through the processingzone of one processing equipment. When the cylinder is moving, on everypoint of the overall cylinder surface, for every revolution, somecoating thickness f(x) will be applied. At every revolution, everyobserved point A will shift by a shifting step of cylinder d to pointA′, and at a following revolution, it will have a coating thicknesscorresponding to point A′. An overall thickness T, applied at point A,after passing through the entire processing zone, will be obtained bythe sum of values of the plot chart at points with step d. Thissummation is equivalent to the integration of the graph of midpoint rulemethod with step d. For another point B, there is the same summation,but by another point selection. Meaning that for every point, theevaluation of fully applied thickness is given by T₀=S/d, where S is anarea under the graph. The precision of this evaluation rises with areduction in step proportional to its quadrature. An evaluation of arelative error is given by the expression

${R \leq {\frac{M_{2}}{24f_{cp}}d^{2}}},$where f_(cp) is an average value of f(x), M₂ is maximum value of f″(x).This evaluation is an evaluation of coating thickness non-uniformity atthe conditions of stable operation of process equipment.

When using N identical process equipment, equidistantly positionedaround substrate holders, the previous estimate holds true, referencedfor a single process equipment, which is repeatable, numbering processequipment consequently from 1 to N. Furthermore, for every point, theinlet of k-process equipment will be determined by the total of valuesat points, shifted relative to the first by

$d \times {\frac{k - 1}{N}.}$If we were to combine all points of summation now, then it will meanthat we are summing values at points with step d/N. Meaning that anapplication of such configuration of equipment is equivalent to anintegration N times, and, accordingly, to an improvement N² times.

The required uniformity may be achieved by the following:

several identical process equipment positioned symmetrically aroundsubstrate holders;

several identical process equipment with step S=(m+1/n)*d, where m is awhole number, n is a number of devices, d is a linear shift of asubstrate holder per time of one revolution, may be positioned along theway of substrate holders;

a part of deposition zone may be masked by a lid, controlled externally.

Regarding the uniformity principle, it is necessary to point out that,if required, substrate holders may move through processing chambers withvarious speed and only have a constant speed in the processing zone. Anability to move substrate holders within one processing chamber withvarious speed: even and constant in the processing zone and anotherspeed outside of the processing zone, but within limits of thatprocessing chamber, ensures an optimization of manufacturing linecomponents due to an ability to use the required, in accordance withdesign, processing chambers, which in turn will increase themanufacturing line productivity.

BRIEF DESCRIPTION OF DRAWINGS

This group of inventions is illustrated by drawings, where:

FIG. 1 shows the distribution graph of the applied thickness per onerevolution from a single processing device, shown on the graph(coordinates along the X-axis in mm, from the center of the device);

FIG. 2 shows substrate holders in a block diagram;

FIG. 3 shows the front view of substrate holders;

FIG. 4 shows components of the magnetic coupling in a block diagram;

FIG. 5 shows the front view of the magnetic coupling;

FIG. 6 shows the general drawing of the manufacturing line.

IMPLEMENTATION OF THE GROUP OF INVENTIONS

The proposed application of thin film coatings on substrates may berepresented by an example of arrangement of process equipment line toapply the four-layer antireflective coating on glass. Layer uniformityrequirements are ±1% for the first and second layer, and ±3% for thethird and fourth layers.

The length of a substrate holder is 100 cm. The movement speed ofholders in the processing zone is determined by the cycle of the lineand is 1 m/min. To apply coating, four processing zones wereestablished, one zone per each layer. Medium frequency magnetrons with800 mm target distance were used as process equipment. The number ofprocess equipment is determined by manufacturing requirements and layerthickness. One process device 01 is used to apply the first layer(magnesium oxide), two process devices 02 for the second layerapplication (titanium oxide), four process devices of each of 03 and 04to apply third (magnesium oxide) and fourth (titanium oxide) layers,respectively.

Since first two layers have stricter uniformity requirements, and asmall number of process devices are used to apply the first layer, theneeded rotational velocity for uniformity will be determined by thefirst layer.

An example of distribution of applied thickness per one revolution froma single process device is shown on the graph (FIG. 1), where X-axis isin mm from the center of the device.

According to the shown graph, the length of the processing zone is 120cm, while the length of border zones, where the thickness is reduced tozero, is approximately 10 cm.

At two revolutions of the substrate holder, while passing through theprocessing zone, the non-uniformity is approximately ±35%: the minimumthickness will be at a point, which will be at an edge and at a centerof the processing zone, and the maximum thickness will be at one of thepoints, which will be subjected to the processing zone twice. A ratio ofthese thicknesses is roughly 1:2, which yields ±33% non-uniformity.

To achieve the required uniformity, it is required to reduce this valueby 35 times, which will yield 2*√{square root over (35)}≈12 as anevaluation of required number of revolutions.

A more precise evaluation by the graph shows that at such a number ofrevolutions, the non-uniformity will be ±0.8%. Based on that, therotational velocity of the substrate holder will be defined so thelinear shift of the holder per one revolution should be no more than120/12≈10 cm. At 1 m/min of forward movement speed, the rotationalvelocity will be at least 10 rpm. Other layers will have a betteruniformity, since an application of two or more identical processdevices is proportionally equivalent to an increase in rotationalvelocity, i.e. an improvement in uniformity.

An operation of the proposed manufacturing line may be represented by anexample of an inline arrangement with a two-stage airlocking, includinga substrate holder, vacuum lock, inlet airlock chamber of low vacuum,inlet airlock chamber of high vacuum, inlet buffer chamber, processingchamber, outlet buffer chamber, outlet airlock chamber of high vacuum,outlet airlock chamber of low vacuum, transportation system with drivingrollers, high-vacuum pumps and process equipment.

The substrate holder consists of the drum (1), with bearings on thecarriage (2). The substrates, for example, are held on plates (3) by anyknown method, which would ensure their reliable fastening during thedrum rotation. The carriage is equipped by guides (10), positioned underthe drum and installed on stands (11) made from a dielectric material.

In many cases, depending on the utilized manufacturing process, thecarriage (2) may be designed in the following way:

as a cart, where linear guides are positioned under the drum;

suspended in air, where linear guides are positioned over the drum;

as a frame, where linear guides are positioned along the sides of thedrum.

or in another way that would ensure a linear movement of the rotatingcylinder.

Components of the removable magnetic coupling (4) and (5) are installedon the ends of the drum shaft. The coupling design is widely known. Afirst component of the removable coupling (4) consists of the softmagnetic hollow material, and magnets (6) are installed along its innersurface. Magnets are installed with alternating polarity, withmagnetization direction shown on the drawing. The mating component ofthe magnetic coupling (5) consists of the soft magnetic cylinder withmagnets (7), installed on its surface, the number of these magnetsmatching the number of magnets of the first component. Magnets areinstalled with alternating polarity, with magnetization direction shownon the drawing. There is a 5 mm gap between the magnets of the first andsecond components, which ensures that there is no contact when thecoupling is rotated in cases of imprecise connection of substrateholders. A direct action electric motor is used to maintain the rotationof the drum. The motor actuator rotor (8) consists of the ring magnetwith magnets on it. The motor actuator stator (9) with control unit ispositioned on the carriage frame. The electric motor's power is suppliedby direct current through linear guides of the carriage (10). For that,linear guides are installed on the insulated stands (11) of thecarriage. The power to linear guides is supplied through thetransportation system's rollers.

The manufacturing line consists of inlet airlock chamber of low vacuum(14), inlet airlock chamber of high vacuum (15), inlet buffer chamber(16), processing chambers (17) with process devices within them, outletbuffer chamber (18), outlet airlock chamber of high vacuum (19), andoutlet airlock chamber of low vacuum (20). Process devices are installedalong the movement of substrate holders, and the processing zone isdetermined by an area along the movement of substrate holders, whereprocess devices are located, and within limits, where most of theapplied material (more than 90%) by this device is deposited on asubstrate holder.

Furthermore, several of process devices designated for depositing thesame material, which partially or completely cover processing zones, areconsidered as one process device. If needed, some process devices,involved in the layer deposition, may be installed around substrateholders.

The holder (22), with substrates fastened to it, enters the inletairlock chamber (14), after which the door (21) of the airlock chambercloses. After the door closes, the holder retreats and its removablecoupling (4) connects to the mating part of the coupling (23), installedat the rotating shaft of the vacuum entrance, driven by an electricmotor (24), installed on the airlock chamber door.

An electric motor spins the drum of the substrate holder up to therequired rotational velocity. At the same time, the airlock chamber ispumped out to 10-20 Pa pressure.

After suction and drum spinning, a transport lock (25) unlocks, thecarriage holder transfers to the inlet airlock chamber of high vacuum(15), and lock (25) closes. The airlock chamber of high vacuum isequipped with turbo-molecular pumps (26), and suction to <0.01 Papressure occurs in it.

After the suction of the airlock chamber of high vacuum, thetransportation lock (27) is unlocked, the substrate holder transfers tothe inlet buffer chamber (16), and lock (27) closes. Within the bufferchamber, the substrate holder is slowed down to the process speed, andconnects with substrate holder, introduced to the manufacturing line atthe previous step. The magnetic couplings of substrate holdersconnecting, and rotation of the incoming substrate holder issynchronized with rotation of substrate holders (28), passing throughprocess chambers. Inside the process chamber, the power is supplied totransportation system rollers, so the electric motors of substrateholders will maintain drum rotation.

Coating application on substrates occurs inside process chambers (17).During the substrate processing (within the processing zone), the drumrotates and moves evenly along its own axis. Substrate holders movethrough the processing zone with a minimal gap between each other.

Considering that the uniformity is mainly determined by a step shift perrevolution, the ratio of the linear movement speed and rotationalvelocity of substrate holders is set so that every point of the surfaceof the substrate holder would make at least two full revolutions whilepassing through the processing zone. Therefore, the step shift per onerevolution is quite small and allows obtaining high uniformity ofapplied coatings regardless of utilized types of process devices,including linear and precise ones.

The challenge to ensure the required rotational velocity of thesubstrate holder during processing, while simultaneously movinglinearly, may be implemented by one of the following methods:

1. The substrate holder is spun up to the required speed, using anexternal drive in one of the inlet chambers, while the carriage isstationary, and later maintains its rotation due to inertia.

2. Every carriage is equipped with a low-voltage electric motor. Thepower to the electric motor is supplied through transportation systemrollers or individual contact rollers on linear guides of the carriage,insulated from the carriage housing.

3. The substrate holder is spun to the required speed, using an externaldrive in one of the inlet chambers, while the carriage is stationary,and the carriage is equipped by a low-voltage electric motor, which isused to maintain the rotation, and may be low-powered.

To ensure the same rotational velocity for all substrate holders in theprocessing zone, they could be equipped with frictional or magneticremovable couplings, which ensure the transfer of rotation betweenneighboring substrate holders during their movement with minimum gaps.

To apply metal-dielectric and composite metal-dielectric coatings,besides the traditional ones for the pass-through equipment, can use oneof the following methods, namely a multiple times application of thinmetallic and under-oxidized layers with consequent oxidation.

The oxidation, in this case, means any reaction that leads to theformation of a chemical bond, for example, with oxygen, nitrogen,selenium, etc. For that, a special processing zone is formed, whereprocess devices are installed around the holder, to apply one or moremetals, and process device for oxidation, representing a source of anactivated reactive gas (for example, a source of plasma). High vacuumsuction, which ensures the gas separation between process device foroxidation and process devices for metal application, is installed in theprocessing zone.

When passing through this processing zone, every point of the processedsurface passes many times through process devices that apply metals,where a super-thin material layer is applied, and passes through aprocess device for oxidation, where this layer is subjected to a fulloxidation. After passing the processing zone, the processed surface isevenly coated by metal-dielectric or composite metal-dielectric coatingwith a specified content.

Process devices may apply one or assorted materials. In the latter case,the speeds of applying materials may be set differently to obtain arequired coating content.

After passing through process chambers (17), the substrate holder entersthe inlet buffer chamber (18).

The transportation lock (29) opens, the substrate holder speeds up,distancing itself from another substrate holder, following it, and movesto the inlet airlock chamber of high vacuum (19); after which, the lock(29) closes, the transportation lock (30) opens, and the substrateholder moves to the outlet airlock chamber of low vacuum (20), where thefront component of the magnetic coupling of the holder connects with themating component of the magnetic coupling (31), installed on the door.The magnetic coupling component (31) is installed on the shaft, whoserotation is made difficult due to friction.

The lock (30) closes, desiccated air is pumped into the chamber, and thepressure is raised to atmospheric. At the same time, due to the brakingof the coupling (31), the substrate holder drum stoppage occurs.

After the pressure in the outlet airlock chamber (20) becomes equivalentto atmospheric, the chamber door (32) opens, and the substrate holderexits the manufacturing line.

The following are claimed:
 1. A method of applying thin film coatings onsubstrates comprising substrate holders and consequent movement ofsubstrate holders through process chambers of a manufacturing linecomprising the following steps: (a) Fastening a substrate to a substrateholder (22); (b) the substrate holder enters an inlet airlock chamber(14) of low vacuum of the manufacturing line, after which a first door(21) of the airlock chamber closes; (c) a removable coupling al of saidsubstrate holder connects to a mating part of a coupling (23) installedon a rotating shaft of the first door of the airlock chamber, saidrotating shaft being driven by an electric motor (24) installed on saidfirst door of the airlock chamber; (d) an electric motor (24) spins adrum of the substrate holder up to a predetermined rotational velocity,while the inlet airlock chamber of low vacuum (20) is pumped out to10-20 Pa pressure; (e) after suction and drum spinning, a firsttransport gate (25) unlocks, and the substrate holder transfers to afirst inlet airlock chamber of high vacuum (15), and the first transportgate (25) locks; (f) the first inlet airlock chamber of high vacuumemploys turbo-molecular pumps (26) to suck air to <0.01 Pa pressure; (g)after the suction of the first inlet airlock chamber of high vacuum iscomplete, a second transport gate (27) unlocks and the substrate holdertransfers to an inlet buffer chamber (16), and the second transport gate(27) locks; (h) within the inlet buffer chamber (16), the substrateholder is slowed down to a process speed, and connects with anothersubstrate holder introduced to the manufacturing line from a previousstep; (i) magnetic couplings (4, 5) of the substrate holders connect,and rotation of the incoming substrate holder (22) is synchronized withthe rotation of the substrate holder or holders (28) from previoussteps, all passing through process chambers; (j) power is supplied totransportation system rollers inside the process chambers, so theelectric motors of substrate holders maintain drum rotation; (k) thecoating application on the substrate holders (22, 28) occur insideprocess chambers (17) in a processing zone where the drum rotates andmoves evenly along its own axis; (l) after passing through theprocessing chambers (17), the substrate holder (22) enters an outletbuffer chamber (18); (m) a third transport gate (29) unlocks and thesubstrate holder speeds up to distance itself from a later substrateholder from a subsequent step, moving to a second inlet airlock chamberof high vacuum (19); (n) the third transport gate locks and a fourthtransport gate unlocks, and the substrate holder moves to an outletairlock chamber of low vacuum (20); (o) in the outlet airlock chamber oflow vacuum, a front component of a magnetic component of the substrateholder connects with a mating component of a magnetic coupling installedon a shaft of a second door of the airlock chamber, said connectionslows down the substrate holder drum until it stops due to friction fromthe mating component; (p) the fourth transport gate closes, desiccatedair is pumped into the outlet airlock chamber of low vacuum, andpressure is raised to atmospheric; and (q) once the pressure becomesatmospheric, the second chamber door opens and the substrate holderexits the manufacturing line.
 2. The method of claim 1, wherein thesubstrate holder makes at least two full rotations while passing throughthe processing zone.
 3. The method of claim 1, wherein the electricmotor is a direct drive motor.